The present invention addresses the pressing need to be capable of surgically excising surface lesions with a discrimination of tissue to be removed/tissue to remain at the millimeter level. Using the principal of Doppler shift, the process and apparatus disclosed discriminates desirable from undesirable tissue by the degree of small vessel blood flow at the surface, with a resolution limited only to the width of the scanning laser Doppler beam. This degree of surgical resolution or precision has never been remotely approached by a surgeon wielding a scalpel.
Incumbent upon any "tangential excision" of surface lesions is the ability to remove the lesion without hemorrhaging the patient to death, a real world concern and rate limiting step with this type of surgery. The process and apparatus disclosed works bloodlessly by virtue of the cauterizing effects of the ablating laser beam. Bloodless tangential excision would allow the scope of an excision not to be limited by blood loss, but by the endurance of the operative team. The present inventor is unaware of such bloodless tangential excision having been realized heretofore.
A very fitting application for the disclosed process and apparatus is the immediate (vs. early) excision and grafting of major burn injuries. Again, the present inventor is unaware of such immediate excision having been realized heretofore. Major burns remain one of the most devastating traumatic injuries, with an annual mortality of &gt;5000 people in the United States (1993), and 80,000 hospitalizations per year. The suffering is especially severe in the pediatric population, where the burns are frequently a result of child abuse.
Early excision and grafting of burns (within five days of injury) has been the principal engine behind improvements in burn mortality over the last twenty years (Effects of early tangential excision and grafting on survival after burn injury. Cryer HG, Anigian GM, Miller FB, et al. Surg Gynecol Obstet 1991 Dec;173(6):449-53). Because of the intensity of the physiologic derangements resulting from burns, the period of resuscitation from burn shock has essentially precluded operative excision of the burns, with its attendant massive blood loss (Burn shock resuscitation. Warden GD. World J Surg 1992 Jan-Feb:16(1):16-23).
The burn wound represents a site of life threatening bacterial infection as well as a lost barrier to microorganism infiltration. Immediate excision and closure of burn wounds remains an important goal of current research to improve outcomes (Early, complete burn wound excision partially restores cytotoxic T lymphocyte function. Hultman CS, Cairns BA, deSerres S, et al. Surgery 1995 Aug;118(2):421-9). If immediate and complete excision of clinical burns were possible, it would represent a quantum leap in the standard of care and be the basis for a dramatic increase in survivorship. The present invention permits this very goal to be achieved.
Other significant clinical problems that would be well addressed by the invention include, but are not limited to, management of decubitus ulcers (bed sores), all non-healing ulcers of the skin, and the precise, rapid debridement of necrotizing fasciitis and other mixed synergistic gangrenes. The latter two entities are dreaded aggressive soft tissue infections with high mortalities and limb loss.
Modified with an additional laser "channel" to excite, then quantify fluorescence from fluorescein or rhodamine tagged monoclonal antibodies, the invention becomes useful in the ablation of tumors. Conceptually, this scheme capitalizes on the fact that nearly all cancerous tumors are hyper-vascular relative to normal tissues, a condition that can be identified by Doppler shift (Role of color Doppler imaging in differentiating between pseudocystic malignant tumors and fluid collections. Fornage BD, J Ultrasound Med 1995 Feb:14(2):125-8). The duality of gating control would allow for discrimination of nonspecific fluorescein or antibody binding by "double checking" with blood flow parameters.
Several prior patents exist that describe the use of lasers for the ablation of tissue. None of them disclose or suggest a combination which includes Doppler shift analysis of tissue blood-flow to control or "gate" the ablating laser.
There are five U.S. Pat. Nos. 5,558,432 (Crowley), 5,010,886 (Passafaro et al.), 4,887,605 (Angelsen et al.), 4,785,806 (Deckelbaum), 4,587,972 (Morantte Jr.) that deal with delivery of wave energy (typically a laser) via a flexible catheter into the intra-vascular space to diagnose and/or ablate a cardiovascular lesion. These lesions are either atheromas causing intralumenal obstruction (blockage of arteries), or foci of aberrant electrical activity in the heart (irregular heart beat). The field of these five patents is cardiovascular, intralumenal medicine.
In U.S. Pat. No. 5,608,520 (Fleming), a method of tumor ablation is described using a laser to vaporize target tissue with the resultant spectral analysis of light emitted employed in gating further ablation. Although comment is made to application in Doppler interferometry, Doppler analysis of blood flow and derivative control and gating of the ablating laser is not described, nor a logical derivative of the information and design disclosed.
In U.S. Pat. No. 4,973,848 (Kolobanov et al.), an "analysis beam" is used to excite a fluorescent dye tagged target which then derives control and gating of a "treatment beam". In the preferred embodiment, these two lasers are convergent, and not coaxial (although feasibility of a coaxial light path is remarked upon). The stated fields include industrial materials processing, dermatology, cosmetic surgery, and tumor therapy. No incorporation of Doppler analysis of blood flow in the "analysis beam" appears to be mentioned. Using blood flow as the means of controlling the treatment beam would not be a logical derivative of the design as disclosed.
In U.S. Pat. No. 4,932,412 (Goldenberg), a process of endoscopic or intra-cavitary ablation of tumor is described which depends on recognition of tumor tissue with radio-immunodetection. This analysis is then potentially used to control and gate an ablative laser. The stated field here is gastrointestinal malignancies.
In U.S. Pat. No. 4,672,963 (Barken), a process and apparatus is described in which target tissue is analyzed with two-dimensional ultrasound. Visual control and gating from the ultrasound image then drives ablation with a laser. The preferred embodiment was demonstrated managing a tumor of the prostate gland.
The preceding four US patents all deal with the destruction of tumors or other undesirable tissue with lasers. One aspect which clearly separates these examples of prior art from the present invention is the analysis of tissue blood flow by Doppler shift to control and gate the ablative laser.
Furthermore, in none of these four patents are two lasers combined optically coaxial. The coaxial nature of the present invention is a significant (but not mandatory) design feature of the present invention, in its preferred embodiment.
Furthermore, in none of these four patents is the optical axis manipulated by a precisely controlled mirror, which streamlines the form factor of a physical embodiment of the design, and provides a high gain in collecting returned wave energy.
Lastly, in none of these four patents is the process and apparatus specifically nor easily adaptable to the rapid excision of clinical burns or soft tissue infections in a bloodless fashion, an important design feature of the present invention, in its preferred embodiment. Although use in tumor therapy was described in the prior art, no addressing of that therapy in a bloodless, cauterizing fashion appears to be disclosed.
It is therefore an object of the present invention to provide for a means to tangentially excise burn wounds immediately upon arrival in the intensive care unit, even in the midst of resuscitation from burn shock.
It is further an object of the present invention to provide for a resolution of normal vs. abnormal tissue (burns or otherwise) at the millimeter level, a precision not previously attainable by any method.
It is further an object of the present invention to provide control for a coaxial ablative laser by gating to surface small vessel blood flow determined by Doppler shift.
It is further an object of the present invention to tangentially excise a burn wound or other tissue lesion bloodlessly by using an ablative laser which cauterizes as well.
It is further an object of the present invention to incorporate selectable wavelengths of the Doppler laser so that the depth of blood flow analysis is variable.
It is further an object of the present invention to incorporate selectable beam width, laser power, dwell time adjustment, and scanning raster adjustment for the ablative laser so that the ablation can be fine-tuned to minimize collateral thermal tissue damage.
It is further an object of the present invention to employ control logic so that a re-analysis of blood flow is done after each ablative cycle (nominally 200 .mu.m ablation depth per cycle) to maximize the depth precision of tissue excision.
It is further an object of the present invention to allow for high-pass or low-pass blood flow gating of ablation so that the device may be used to ablate tumors or soft tissue infections characterized by a higher than normal blood flow.
It is further an object of the present invention to allow for insertion of a second diagnostic laser channel set up to excite and detect fluorescence from dye tagged monoclonal antibodies adherent to target tissues. In this mode, gating of the ablative laser would be dual: to blood flow and to presence of fluorescent tagged antibody binding.
It is further an object of the present invention to incorporate adjustments to the ablating laser such that dwell time can be modified by motion dither introduced by ultrasonic vibration of elements in the optical path.
It is further an object of the present invention to employ a control electronics suite and logic sufficient to permit treatment of the whole surface area of an adult in the span of several hours.
It is further an object of the present invention to incorporate digital image stabilization to overcome un-preventable patient motion.